In treating certain surfaces and particularly large surfaces on an industrial scale, blasting machines have been employed as a way of efficiently cleaning surfaces particularly where removal of paint, rust, or other undesirable surface material is required. Such blasting machines typically include a unit having a blasting wheel for propelling abrasive material against the surface to be cleaned. The blasting area or zone to which the abrasive is propelled is substantially enclosed such that the abrasive, as well as the surface material removed by the abrasive, are not unduly expelled to the surrounding atmosphere. In communication with this enclosure is a system for receiving the spent abrasive and returning it to the blasting wheel for recycling in cleaning the surface being treated.
On relatively horizontal surfaces these blasting machines can be moved and operated quite readily by hand, cars, trucks and the like. When treating surfaces which extend substantially towards a vertical direction, the apparatus for moving the machines has become more complex. Often for large storage tanks and ship hulls, a special structure has been developed which suspends the blasting machine on the side of the surface to be treated and lowers the machine along a prescribed path vertically and, in addition, moves the machine horizontally to abrade and clean the surface being treated. This type of apparatus involves either maintaining portions of the machine-supporting and manipulating structure on each surface to be treated, or rebuilding a structure on the surface each time it has to be cleaned by the blasting machine. This is not only an expensive and time consuming proposition, it often requires the placing of rails or other guiding devices in an unsightly fashion on the surfaces to be treated to insure the proper movement of the blasting machine.
There have been some portable structures which have adopted mechanisms for moving the blasting machine across the working path along the vertical surface without the need to relay on tracks and other structures mounted on the surface. However, the devices developed thus far are rather awkward in their operation and require undue operator control to maintain the correct position and contact of the blasting machine with the surface being treated. This is true particularly where the surface is not flat but is round or has indentations and, as a result, the disposition of the blasting wheel must change several times relative to the surface being treated during its movement through a working path. Such devices have included magnetic or vacuum mechanisms which are cumbersome and often require some additional supporting structure. In addition, some of these devices have required that the blasting wheel be located in a position somewhat remote from the area being cleansed. This of course results in additional loss of abrasive velocity durings its travel along the extra distance from the wheel to the surface, and even prevents such a system from being used on surfaces that are high above the ground.
Some other portable devices such as that shown in U.S. Pat. No. 3,908,314 to Watanabe et al., have incorporated a telescopic boom on a swingable frame for moving a blasting machine through a path along the surface being treated. An expandable frame carrying the blasting machine is located on the end of the telescopic boom. To place the machine in contact with the surface disposed at an angle to the vertical, the operator must control movement of the machine into the correct disposition. In this operation one of the frames moves on another through the action of a series of ropes and pulleys to provide proper machine orientation with respect to the angled surface being treated. During movement of the machine through the working path, the burden falls on the operator to make the necessary adjustments and insure that the blasting machine is maintained in the correct disposition as it moves along the surface.
The present invention largely avoids problems which have characterized the use of blasting machines to treat surfaces that are in a substantially inclined to the vertical plane. A simple but effective mechanism has been devised which achieves the desired disposition of the blasting machine adjacent the surface as it moves through a blasting path or swath, regardless of surface angle to the vertical and with minimal effort by the operator. Once the blasting machine is placed in a correct disposition adjacent the surface and motion initiated through the working path, the orientation of the blasting machine will be automatically adjusted to compensate for changes in the surface configuration as the machine is moved along the working path.
For this purpose a portable support structure is provided adjacent, but essentially unsupported by, the surface to be treated and has a telescopic boom extending from the support structure. The distal end of the boom has a blasting wheel device capable of being moved in various rotatable and pivotal directions. A series of sensors are positioned in the vicinity of the blasting zone of the blasting machine to sense the position of the machine relative to the surface being treated. These sensors are integrated with means on the distal end of the machine, as well as means located near the support structure for articulating and otherwise adjusting the position of the machine depending on the angle or curvature of the surface sensed.
The mechanism described herein provides for two principal modes of operation, among others. In a first mode a truck acting as a support structure can be parked parallel to the surface being blasted and far enough away that the boom when retracted can be positioned over the side of the truck. The blasting machine will be held in proper relationship to the surface being blasted while the machine is moved through a vertical swath or other working path. To blast through a new swath the operator can rotate the boom to the next position, typically adjacent the path previously blasted, and move the machine through another working path which may be coextensive with the previous path. A second mode of operation can be used particularly in those cases where there is insufficient room to rotate the retracted boom over the side of the truck. In this situation the truck can be parked close to the vertical surface, and the boom moved until the blast head contacts the surface with the boom over the corner of the truck adjacent the surface. The blast head is then held in the proper relationship to the surface as the operator controls the extension and elevation of the boom to blast successive arcs or other geometric patterns on the surface treated.
Because of the flexibility of the boom with the large mass on its end, the precision of positioning the blasting machine by the controls may be limited. Consequently, the frame, which defines the blasting zone, can be allowed to float relative to the remainder of the blasting machine and may be spring loaded by, for instance, air cylinders in order to bias the floating frame toward the surface to be treated. An elastomer seal surrounds the blasting zone for engaging the surface being treated and thereby preventing undue expulsion of abrasive to the surrounding atmosphere. Adjustable casters on the floating frame extend toward the surface to be treated and prevent crushing of the elastomer seal by the force from the air cylinders.
With the various features of the present invention, which will more clearly be appreciated in the preferred embodiment described hereinafter, the problems mentioned above with prior blasting devices have been overcome at least to a large extent. The sensing mechanism along with the system for moving the blasting wheel eliminates a substantial amount of what otherwise would be operator controlled effort. In addition, the articulating mechanism avoids the rather cumbersome and unreliable system of multiple frames and tracks along with pulleys and chains or cables which have characterized other more or less portable systems.